Fluid heat exchange apparatus



May 5 1942. J, H B 2,281,580

FLUID HEAT EXCHANGE APPARATUS Filed Oct; '28, 1938 5 Sheets-Sheet l 1NVENT OR.

Hobbs M y' 5, 1942. J. c. HOBBS 228L580 FLUID HEAT EXCHANGE APPARATUSFiled Oct. 28, 1938 Fig: 2

5 Sheets-Sheet 2 INVENTOR.

3 James Cflobbs I May 5, 1942. J, HOBBS 2,281,580

FLUID HEAT EXCHANGE APPARATUS Filed Oct. 28, 1938 5 sheets -sheet 4INVENTOR. v

f N James C Hobbs ATTORNE y 1942- J. c. HOBBS 2,281,580

mm) HEAT EXCHANGE APPARATUS Filed om. 28, 1938 5 Sheets-Sheet 5 Fig 6-INVIENTOR. James C Hobbs Patented May 5, 1942 UNITE S'E'A'I'Efi PATENTOFFICE 2 Claims.

The present invention relates to fluid heat exchange apparatus, and itmay be considered as exemplified in a steam superheater.

Present day steam boiler installations are provided with superheaters,and, in the more effi cient plants operating at high pressures, thetemperature of the steam is high enough to involve dimculties inavoiding damage to the superheater metal. The superheaters usuallyconsist of a multiplicity of similar tubes through which steam flowsfrom an inlet to an outlet header, the tubes being disposed in a gaspass through which gases of combustion flow and from which the heat ofsuperheat is derived by transfer through the tube walls.

The steam flowing through the tubes in parallel should absorb heat fromthe gases in such amounts that the steam temperature will be the same atthe outlet ends of all of the tubes. Also, if the individual superheatertubes are supplied with the same amount of steam by uniform division ofthe whole flow between them, then each tube should absorb the sameamount of heat from the gases. For this to be possible there must beequalization of gas flow rates past each tube and equality oftemperature in the gases approaching the tubes. This is equivalent tothe requirements that the gas flow shall be equally distributed over thecross section of the gas stream and that the gases shall be at the sametemperature over that cross section.

To fulfill these requirements of uniform gas flow and temperature over across section of the gas stream at the entrance to the superheater zoneis extremely difiicult, and, in many cases, it is quite impossible. Thisinvention, accordingly, seeks to accomplish the desired results in spiteof these conditions.

If the steam flows from a plurality of tube outlets vary as totemperature, yet when mixed together in an outlet header a desiredaverage temperature is attained, there are differences in theeffectiveness of the heat absorption of the various tubes. Some of thetubes absorb heat at lower rates than others, while the latter may evenbe attaining or approaching a steam or tube metal temperature which ishazardous. It is the aim of this invention to so co-ordinate positionsof the various tubes with reference to the heating medium thatequalization of heat absorption and consequently equalization of steamtemperature is more nearly approached.

There are two main causes of inequality ,of gas flow and temperatureover a cross section of the gas stream approaching the superheater. Oneof these originates in combustion conditions in the furnace, and theother in the form of the gas flow path within the enclosing wallsbetween the furnace exit and the entrance to the superheater zone,especially as to changes of direction.

: p r a ow rsroup If the gases leave the furnace horizontally and thenflow vertically to the superheater zone there is a tendency for the flowto concentrate at the outside of the, turn. There is also ,a tendency toset up eddy currents, and even a reverse flow may exist in one part ofthe gas duct with a steady direct flow in another. In addition, whenwater cooled gas boundary surfaces are present inequality of gas flowwill result in inequality of heat transfer rates and gas temperatures atthe entrance of the superheater zone even if the velocity andtemperature of the gases are equal over the cross section of the streamleaving the furnace.

If the combustion conditions across the furnace are unequal as to rateof combustion per unit of width of gas exit, or are unequal as to excessair, or both, the gases may vary in temperature and velocity over thearea of the exit, and this inequality will continue up to the entranceof the superheater zone, subject to further disturbances due to flowconditions over the gas path.

Another cause of inequality of gas temperature and velocity at thefurnace exit, which may persist up to the superheater zone, arises fromthe location of the burners, their adjustment, and. other operatingconditions. If the, burners are concentrated near the center of a widefurnace, the gases leaving the furnace exit near the side walls may havevelocities or temperatures lower than the gases leaving the central partof the furnace. This would especially be the case if the exit werecharacterized by large area for low draft loss. If, on the other hand, aplurality of burners are arranged in a row extending all the way acrossa wide furnace, then, differences in the adjustments of the burners, ordiiferences in their capacities may cause inequalities of gas velocityor temperature over the cross section of the furnace, particularly alonga line parallel to the line of the burners.

My invention solves the problem of equalizing the temperature of steamleaving the several superheater tubes in spite of such inequalities ofvelocity and/or temperature of the gases approaching the superheater.

Illustrative embodiments of my inventionv are disclosed in theaccompanying drawings, in which:

Fig. l is a vertical section of a. steam boiler which includes theillustrative superheater;

Fig. 2 is a vertical section of part of the-Fig. 1 boiler with certainparts broken away t0 Show the superheater on an enlarged scale;

Fig. 3 is a vertical section takenlon the line 3-3 of Fig. 2;

Fig. 4 is a horizontal section takenhon @the line 4-4 of Fig. 2- andshowing thev cross-over connections for the superheater coils of the up-Fig. 5 is a diagrammatic view illustrating another modification of theinvention; and

Fig. 6 is a multiple horizontal section on the broken section line 6-6of Fig. 1.

The installation indicated in Fig. 1 of the drawings includes thefurnace I0, the walls of which are defined by steam generating tubesconnected into the boiler circulation. The furnace is fired by aplurality of burners I2, I4, and

I6 which are adapted to burn pulverized fuel.

The gases of combustion leave the furnace through the exit I8 and passupwardly over the tubes of the superheater positioned in the gas pass22. The superheater consists-of spaced tubes extending across the gaspass, these tubes being bent so as to form fiat coils. The coils areassembled in the gas pass 22 side by side, and are disposed in spacedarrangement over the whole width of the pass between opposite walls,each individual coil extending across the gas pass between the remainingopposite walls. The preferred relationship between the superheater tubesand the gas fiow is such as to cause the gases to fiow transversely ofthe tubes and in a direction parallel to the planes of the fiat coils.

The superheater coils are arranged in two groups, an upper group 24 anda lower group 26, the groups presenting tube banks over which thefurnace gases fiow in succession. The flat coils of one group areconnected to those of the other so that the steam flowing through a flatcoil of the upper group flows through a flat coil of the lower groupwhich is disposed in a different plane longitudinall of the gas pass.The relative po sitions of the two planes occupied by the two flat coilssuccessively traversed by the steam and the gases are determined withreference to the mean velocities or temperatures of the parts of the gasstream in which the planes are disposed, so as to substantially equalizethe amounts of heat absorbed by the steam passing through a plurality offiow paths formed by such pairs of connected flat coils. Considering oneof these flow paths, if the fiat coil of the first group 24 is disposedin a plane where the gas flowing past it has a Velocity or temperaturelower than in other planes, the second group fiat coil forming a part ofthe same fiow path would be disposed in another plane where the gasesflowing past it are higher in velocity or temperature. In this way thevariations of gas temperature and velocity across the gas stream andalong the row 1 of flat coils are not reflected in temperaturedifferences in the steam leaving a plurality of such flow paths, but onthe contrary, the effect is to equalize such temperatures.

The desired relative positions of the planes of the connected first andsecond group flat coils may be predetermined from a knowledge of thedistribution of gas as to velocity and temperature over the streamsection, or it may be determined from observations of steam temperaturesat the outlets of the individual flat coils, which, if found to be atundesirable values, may be corrected by changing the cross-overconnections between sections of the first and second group coils.

In the preferred embodiment of my invention a space is left between thefirst and second groups of superheater coils and in this space arelocated the cross-over tube connections for the pairs of fiat coils.This space also has the advantage of providing access to the cross-overconnections for changing the relative positions of the planes of theflat coils. This space is indicated at in Fig. 2 of the drawings, andthe manner in which the cross-over tubes are disposed in that space isindicated in Figs. 2, 3, and 4.

Steam flowing from the drum 32 through the supply tubes 34 and 36 to thecoils 38, 40 and 42 of the first group 24 passes through the downwardlyextending parts 44, 46, and 48 (see Fig. 3) of the cross-over tubes at aposition near the side of the superheater gas pass adjacent thesuperheater outlet header 50. From this position it passes transverselyof the gas pass to the coils 52, 54, and 5B of the lower group 26. Thepaths for this steam flow are afforded by the transverse sections 58,60, and 62 of the cross-over tubes, these transverse sectionscommunicating at their opposite ends with the downwardly extending parts64, 60, and 68 of the cross-over tubes.

Considering Figs. 3 and 4 of the drawings, the coils above indicated at38, 40, and 42 are the first, third, and fifth coils of the upper group24. Coils I0, 12, and I4 are, respectively, the second, fourth, andsixth coils from the left-hand wall I5 of the gas pass I8. The latterare separately connected to the second, fourth, and sixth coils 80, 82,and 84 of the lower group 26 by cross-over connections which include thetransverse tube 5 80 and two companion tubes directly below it.

by the downwardly extending connections 86, 88,

The coils I0, I2, and I4 are connected to the transverse tube 90 and itscompanion tubes (in the same horizontal planes as the tubes 58, 80, and02, and therefore not appearing in Fig. 3)

and I00, and it will be noted that the transverse tube 90 and itscompanion tubes leading from these downwardly extending sections, havetheir axes in a vertical plane adjacent the gas pass 1 wall defined bythe water tubes I02 and the blocks I04 closing the spaces between thosetubes.

At the right-hand ends of the transverse tube 80 and its companion tubesthere are the downwardly extending sections I06, I08, and I I0 whichdirectly communicate with the tube sections H2, H4, and H6 of the coils88, 82, and B4 of the lower group of superheater coils 26.

Similarly, steam flowing through the coils I20, I22, and I24 of theupper group of superheater coils passes through cross-over tubeconnections w gas pass.

which include a corresponding number of transverse tube sections I26 tothe coils I28, I38, and I32, and this system of cross-over connectionsis continued in each of the superheater gas passes I8 and I40 so that,for instance, the coils of the upper group 24 at one side of the gaspass are individually and directly connected to the coils of the othergroup 26 at the opposite side of the Thus, approximately half of thecoils of the upper group adjacent the gas pass wall the gas pass wallI44.

I42 of the gas pass I40 are individually and directly connected to thecoils of the lower group 26 at the opposite side of the gas pass andadjacent The remaining coils of the first group 24, at the side of thegas pass I40 and adjacent the wall I42.

upper group 24 in zones of lower gas velocities and temperatures. Inthis way the individual steam flows will have their temperaturessubstantially equalized at their outlets.

In the embodiment of the invention illustrated in Figs. 1, 2, 3, 4, and6 of the drawings the burners 12, I4, and I6 are grouped centrally ofthe furnace and the furnace gases passing from the exit I8 and from thegas pass 22 may be at higher temperatures and higher velocities at thecentral part of the installation. In this arrangement, higher gastemperatures and higher gas velocities would exist adjacent the gas passwalls 16 and I42 of superheater gas passes 18 and I40 a above indicated,and the cross-over connections for the coils of the upper and lowersuperheater groups are arranged so as to compensate for suchinequalities. In this particular installation, there is an additionalgas pass between the walls 16 and I42, but this is occupied by theeconomizer sections I50, I52, and I 52. However, if the illustrativeinstallation were modified so as to have a superheater extendingentirely across the width of the installation in a single gas pass, itis within the scope of the invention that the superheater coils bearranged and connected as indicated in Fig. of the drawings. Here, thecentral coils a and a of the upper group I60 are disposed in a zone ofhigher gas velocities or higher temperatures and are therefore joined bythe cross-over connections I63 and I35 in the space I62, with coils a"and 11 adjacent the gas pass wall I64 and I86 respectively, and in zonesof lower gas temperatures or velocities. Conversely, the coils d and din the lower group I68 and in zones of higher gas temperatures andhigher gas velocities are directly joined by the connections I61 and I68with the coils d" and d' of the upper group I 60 located in zones oflower gas temperatures and lower gas velocities. Of the remaining coils,the coil 0 of the upper group is joined by the connection I to the coil0' of the lower group on the opposite side of the gas pass. The coil bis similarly joined by the connection I12 to the coil b of the lowergroup I68. On the opposite side of the upper gas pass the coils c" andb" are joined by the connections I16 and I18 to the coils b' and c' ofthe lower group I68 and on the opposite side of the gas pass I80.

In connection with the illustrative embodiment it will be noted that thecoils of the upper group 24 form a counter-flow superheater sectionwhile most of the coils of the lower group 26 constitute a parallel flowsection, the steam passing upwardly from the straight tube sections 200,202, and 204 through successive return bend coils to the outlet header50. These tube sections 200, 202, and 204 receive steam directly fromthe uppermost return bend coils 206 of the lower group 25. Preferably,the coils of both groups are supported by lugs 2| 0-2I5 inclusive,secured to the wall cooling tubes I02 and 216. Complementary brackets2I1-222 inclusive, welded to the return bends of the superheater coilsco-operate with the lugs to maintain the superheater coils in theiroperative positions, the successive tube sections of the superheatercoils being connected by the hangers such as those indicated at 223-220inclusive, for suspending the lower superheater coils from the uppercoils which have the brackets welded thereto.

The furnace gases after passing over the coils of the superheater groups24 and 26 pass over the tubes of an economizer 250 and then past thedamper 252. The gases are then discharged through a flue, preferably bymeans of an induced draft fan. Secondary air is heated by the furnacegases and it then passes through a duct 210 to the chamber 212 enclosingthe burners.

The circulatory system of the installation indicated in Fig. 1 of thedrawings includes the furnace roof tubes 300, the floor tubes 302, thewall tubes 302, and the headers 303, 308, and 3I0. The furnace sidewalls also are defined by tubes 3| 2 connected into the boilercirculation through the intermediacy of the upper headers 3I4 and thelower header 3I6 and appropriate connections with the drum 32, thespaces between the furnace wall cooling tubes being preferably closed byrefractory blocks similar to the blocks I 04 previously mentioned.

The wall tubes I02 are connected at their upper ends to the water spaceof the drum 32 and at their lower ends to a header 320 to which the walltubes 216 of the superheater gas pass are also connected. The latter arejoined at their upper ends to the header 322 which, in turn, isconnected to the drum 32 by the tubes 324 and 323. Appropriateconnections may be provided for the headers 3I0, 3I6, and 320 at thebase of the installation.

Whereas, I have described my invention with reference to the particularembodiments shown in the drawings, it is to be understood that theinvention is not to be considered as limited to all of the detailsthereof. It is to be considered of such scope that many of these detailsmay be modified, so long as the essence of the invention is retained. Ingeneral, the invention is of a scope commensurate with the scope of thesubjoined claims.

I claim:

1. In fluid heat exchange apparatus, means forming a gas pass forfurnace gas flow having non-uniform heat exchange values over its crosssection, separate and spaced apart tube banks arranged transversely ofthe gas pass with each bank consisting of substantially uniform fiatcoils having their axes disposed in planes extending parallel to thegeneral direction of gas flow, and laterally extending tubularconnections each establishing communication between the outlet of a coilin one bank and the inlet of a coil of the other bank, the latter coilbeing disposed at a different distance from the same side of the gaspass, each of said tubular connections with the coils directly connectedtherewith forming a separate flow path having parts arranged in zones ofdifferent and compensatory heat exchange values, the separate flow pathsbeing arranged in parallel.

2. In fluid heat exchange apparatus, means forming a pass for a furnacegas flow of nonuniform heat exchange values over its cross section, aplurality of spaced apart tube banks extending across the gas pass, saidbanks of tubes being spaced apart in the direction of gas flow, eachbank of tubes consisting of flat return bend coils with their axes inplanes substantially parallel to the walls of the gas pass, and tubularmeans in the space between the banks of tubes, each of said meansforming a separate fluid path by the connection of the outlet of a coilof the first bank of tubes to the inlet of a coil of the second bankdisposed in a different longitudinal zone of gas flow, the coils joinedby each of said means being disposed in zones of different andcompensating heat exchange values.

JAMES C. HOBBS.

